The San (Polish: San; Ukrainian: Сян; German: Saan) is a river in southeastern Poland and western Ukraine, a tributary of the Vistula River, with a length of 443 km (it is the 6th-longest Polish river) and a basin area of 16,861 km2 (14,390 km2 of it in Poland).

The San valley must have become an important trade-route and axis of human settlement as early as the 9th or 10th century.[citation needed] The region subsequently became part of the Great Moravian state. Upon the invasion of the Hungarian tribes into the heart of the Great Moravian Empire around 899, the Lendians of the area declared their allegiance to the Hungarian Empire. The region then became a site of contention between Poland, Kievan Rus and Hungary starting in around the 9th century. This area was mentioned for the first time in 981 (by Nestor), when Volodymyr the Great of Kievan Rus took the area over on his way into Poland. In 1018 it returned to Poland, in 1031 reverted to Rus, and in 1340 was recovered by Casimir III of Poland.

During the years 966–1018, 1340–1772 (the Ruthenian Voivodeship) and 1918–1939, the region was part of Poland. Between 1772 and 1918 it belonged to the Austrian empire, which became the Austro-Hungarian empire when the double monarchy was introduced. This region, including the area west and east of the Subcarpathian Voivodship, was controlled by Austria for almost 120 years. During that time it was known as Galicia.

The San River, which saw many battles in its history, was a battle site during the start of World War II in Europe. At the outset of the German invasion of Poland, Polish forces attempted to defend a line along the San from September 6, 1939, until German forces broke out of their bridgeheads on September 12, 1939.

^"It is possible to separate the group of La Tène culture (Celtic settlement) in the Upper Tisza Basin. For the time being there are about 160 sites noted. They can be divided into several distinct categories which include the following: settlements, production areas, sepulchral sites, i.e., burial grounds and single graves as well as various hoards (deposits of coins and tools). Moreover, there are three oppida: Zemplin, Bükkszentlászló and Galish-Lovačka. The chronology of the whole group lies between LT B1-LT D1/D2. Especially interesting is the problem of correspondence between this group and the group of sites in southeast Poland. Material connections are also documented in ancient sources. They allow to identify the group from Upper Tisza as the Anarti tribe and the group from southeast Poland as the Anartophracti, which is a part of the former." [in:] Marek Olędzki. La Tène culture in the Upper Tisza Basin =La Culture de la Tene dans le Bassin de la Haute Tisza. Ethnographisch-archaeologische Zeitschrift. ISSN 0012-7477